The event in question is Touhou Kamuisai 7, a regional Touhou event which was scheduled to be held in Sapporo on February.

However, the event’s organisers report police and the venue forced them to cancel as a result of what happened at Comiket and missives sent to the event itself:

As a result of the influence of the threats, due to various circumstances our venue, the Teisen Hall (mostly used for pro-wrestling it would seem), contacted us to discuss suspending the event.

We discussed the matter with them, but the demands of the venue and local police to cancel the event were so strong we had no choice but to cancel.

Further clarification of this excruciatingly vague explanation was forthcoming after speculation about the nature of the threat (it was thought the event might have been cancelled just because of what happened with Kuroko) ran rampant online:

Unfortunately, our explanation of it being due to ‘various circumstances’ caused much confusion. This was inexcusable.

[…]

The reason for the cancellation was that the Kamuisai itself received threats.

Without going into details as to the content of the threat the Teisen Hall reported receiving, there was a threat against the event and the police and venue’s operators then demanded we cancel it.

We did discuss a plan involving heightened security with guards and baggage checks, but as there is bowling alley next to the venue, it was decided it should be cancelled out of concern for the safety of those patrons.

They also formally reported the incident to police, but if their record in similar cases is anything to go by not much can expected from them – despite the culprit actually attending Comiket and leaving threatening letters in the hall, they have still yet to announce any progress.

There is considerable suspicion that the event’s cancellation is a direct result of the precedent set by Comiket in yielding completely to the terrorist threats it received, and that now any such event is entirely at the mercy of crazies sending threatening letters to their venue:

“Just as expected…”

“They gave in?”

“Obviously a copycat inspired by what happened at Comiket.”

“Expect more. The police probably want to eradicate doujin events in any case.”

“First Kuroko fans, now Touhou otaku…”

“I don’t care about this event, but you can’t just give in like this. It’s inviting more of the same.”

“There is actually a Kuroko event at the same venue two weeks earlier.”

“So the Kuroko fujoshi and Touhou otaku are squaring off against each other…”

“How useless are the police for allowing this stuff to go on?”

“That area is now the most unsafe part of Sapporo, so it’s obvious that station is staffed by total incompetents.”

“Our police are too busy forcing people accused of brushing up against schoolgirls to confess to groping to bother with such inconsequential matters.”

“The cops are desperate to shut these events down and with Abe and his cronies back in things are only going to get worse.”

“They aren’t even investigating this stuff. Unless something actually happens they will do nothing.”

“Just because they have not said or done anything doesn’t mean they aren’t investigating this at all, does it?”

“This is exactly what the criminal wanted… now all these events are vulnerable to random cancellations because of threats like this.”

“Everyone was saying Touhou would be next, but because they were just a bunch of fujoshi the first time nobody took things seriously. Somebody is just going to start sending letters to every event and that will be the end of things.”

First they came for the Kuroko doujins, I did not speak out because I was not a fujoshi.

Then they came for the Touhou doujins, I did not speak out because I was not a Touhou otaku.

Then they came for the rape and guro doujins, I did not speak out because I was not into rape and guro.

And when they came for the ordinary doujins, there was no one left to speak for me.

In other words, you 2ch otakus should stop moaning and actually start a protest or something. You were so fired up in your anti-Korean and anti-Chinese protests, so why can't you do the same for something that you actually like?

Please do so. It would be interesting to see how they react to a counter-threat. If they so easily drop their pants and bend over to accomodate one 'terrorist', I suppose they would be most happen to wet their lips and BJ the other.

It's probably easier to ban the event than searching for a culprit (it is less work and easier for police so busy looking suicidal and molesters of little girls):\
Maybe it was the Ishihara, was dismissed as the only way to ruin events is by letter of threat.
Hopefully the otakus find this troll and give this sucker a lesson!!